1 of resident lipid transfer proteins, namely
saposins.
2 tion site are strictly conserved in all four
saposins.
3 me cases, by lipid transfer proteins such as
saposins.
4 t sphingolipid-activating proteins (SAPs) or
saposins.
5 ns into a critical cysteine in each of these
saposins.
6 Individual
saposin A (A-/-) and saposin B (B-/-)-deficient mice sho
7 Saposin A (SapA) lipoprotein discs, also known as picodi
8 the nonsignal NH2-terminal peptide preceding
saposin A (termed Nter) was usually removed prior to sap
9 d saposins C and A, wild-type saposin C, and
saposin A [Y30A], poorly with saposin C [A31Y], and not
10 In the absence of lipid,
saposin A adopts a closed monomeric apo conformation typ
11 osed of human sphingolipid activator protein
saposin A and a small number of phospholipids, to displa
12 Saposin A and B proteins were undetectable in AB-/- mice
13 By site-directed mutagenesis of
saposin A and C, their membrane topological structures w
14 nted using picodiscs (complexes comprised of
saposin A and lipids, PDs), to screen mixtures of glycol
15 A (termed Nter) was usually removed prior to
saposin A cleavage.
16 Saposin A contains an additional glycosylation site and
17 hat, in addition to GALC deficiency, genetic
saposin A deficiency could also cause chronic GLD.
18 Genetic
saposin A deficiency might be anticipated among human pa
19 genic activity whereas reduced and alkylated
saposin A did.
20 an amino acid substitution (C106F) into the
saposin A domain by the Cre/loxP system which eliminated
21 Wild-type
saposin A had no neuritogenic activity whereas reduced a
22 Saposin A has roles in sphingolipid catabolism and trans
23 The structure reveals two chains of
saposin A in an open conformation encapsulating 40 inter
24 tein, we determined the crystal structure of
saposin A in the presence of detergent to 1.9 A resoluti
25 Thus,
saposin A is indispensable for in vivo degradation of ga
26 Saposin A lipoprotein discs exhibit limited selectivity
27 However, no specific
saposin A or D deficiency is known.
28 on of saposin C, and the analogous region of
saposin A showed that more "saposin C-like" molecules ha
29 ic placement of amino acids, and that Y30 of
saposin A significantly alters local conformation in thi
30 Introduction of the conserved
saposin A Tyr 30 (Y30) into saposin C at the analogous p
31 through a tetrasaposin, A-B-C-D, from which
saposin A was then removed.
32 Nondenatured
saposin A with an introduced A30 acquired substantial ne
33 The phenotypic features of
saposin A(-/-) mice are qualitatively identical but mild
34 Saposin A(-/-) mice developed slowly progressive hind le
35 When
saposin A(-/-) mice were subcutaneously implanted with t
36 During intercrossing of
saposin A(-/-) mice, we observed that affected females t
37 ntly down-regulated in the brain of pregnant
saposin A(-/-) mice.
38 s and microglia in the demyelinating area of
saposin A(-/-) mice.
39 chronic form of the disease by inactivating
saposin A, the essential activator of galactosylceramida
40 Those with more "
saposin A-like" spectra did not.
41 osin C [A31Y], and not at all with wild-type
saposin A.
42 with amino acids in the analogous region of
saposin A.
43 These findings indicate that combined
saposins A and B deficiencies attenuated GalCer-beta-gal
44 created by knock-in point mutations into the
saposins A and B domains on the prosaposin locus.
45 n insight into the interrelated functions of
saposins A and B, combined saposin AB-deficient mice (AB
46 iencies of saposins C and D and decreases in
saposins A and B.
47 Saposins A and C were produced in Escherichia coli to co
48 elices at the amino- and carboxyl termini of
saposins A and C were shown to insert into the lipid bil
49 n models are proposed for the membrane-bound
saposins A and C.
50 In comparison, the middle region of
saposins A or C were either embedded in the bilayer or s
51 In C-/- mice, prosaposin and
saposins A, B and D proteins were present at near wild-t
52 Saposins A, B, C and D are derived from a common precurs
53 Sphingolipid activator proteins (
saposins A, B, C and D) are small homologous glycoprotei
54 otein that encodes four glycoproteins, named
saposins A, B, C and D.
55 precursor of four activator proteins, termed
saposins A, B, C, and D, that are required for much of g
56 Prosaposin, the precursor of
saposins A, B, C, and D, was recently identified as a ne
57 Prosaposin, the precursor of
saposins A, B, C, and D, was recently reported to be a n
58 zygotes (B-/-) mice, whereas prosaposin, and
saposins A, C and D were at normal levels.
59 Saposins (
A, B, C and D) are approximately 80 amino acid
60 Saposins (
A, B, C, and D) are small sphingolipid activat
61 Based on the
saposin-
A (SapA) scaffold protein, we demonstrate the su
62 ated functions of saposins A and B, combined
saposin AB-deficient mice (AB-/-) were created by knock-
63 Here we show that
saposins,
although not required for the autoreactive rec
64 We propose that MTP acts upstream of the
saposins and functions as an ER chaperone by loading end
65 res are closely related, suggesting that all
saposins and saposin-like domains share a common topolog
66 Total deficiency of all
saposins and specific deficiency of saposin B or C are k
67 The oligosaccharides on
saposins are not required for in vitro activation functi
68 Saposins are small, heat-stable glycoprotein activators
69 The
saposins are small, membrane-active proteins that exist
70 r proteins SAP-A, -B, -C and -D (also called
saposins)
are generated by proteolytic processing from a
71 Individual saposin A (A-/-) and
saposin B (B-/-)-deficient mice show unique phenotypes c
72 Saposin B (Sap B) is an essential activator protein for
73 Recently, native
saposin B (sapB) has been shown to bind CoQ10 and subseq
74 posins containing various length segments of
saposin B and C localized the neurotrophic and acid beta
75 Patients with kidney disease lacked
saposin B and showed new components in two patterns: the
76 Using
saposin B as a unreactive backbone, chimeric saposins co
77 We found that
saposin B bound to neutral glycosphingolipids and gangli
78 Saposin B could also mediate lipid binding to soluble CD
79 Blocking sulfatide degradation from the
saposin B deficiency diminished galactosylceramide accum
80 Saposin B derives from the multi-functional precursor, p
81 ng and compressing the central cavity of the
saposin B dimer, may play a key role in facilitating lip
82 These findings delineate the roles of
saposin B for the in vivo degradation of several GSLs an
83 ting a compensation in LacCer degradation by
saposin B for the saposin C deficiency.
84 We found that
saposin B forms soluble saposin protein-lipid complexes
85 wed few components other than two ubiquitous
saposin B glycoisoforms.
86 e of SDS is very similar to a monomer in the
saposin B homodimer structure.
87 of B-/- mice supporting the in vivo role of
saposin B in the degradation of these lipids.
88 ore assays we demonstrated that lipid-loaded
saposin B increases the off-rate of lipids bound to CD1d
89 Saposin B is a water soluble alpha-helical protein which
90 The X-ray structure of
saposin B is homodimeric.
91 gher than that of lysosomes, suggesting that
saposin B may facilitate lipid binding to CD1d molecules
92 Because
saposin B must bind lipids directly to function, we foun
93 y of all saposins and specific deficiency of
saposin B or C are known among human patients.
94 Mutations in
saposin B present in humans with phenotypes resembling m
95 No
saposin B protein was detected in the homozygotes (B-/-)
96 be absolutely essential, but the absence of
saposin B resulted in the lowest recognition of alpha-ga
97 Saposin B was also the most efficient in mediating alpha
98 were added to the prosaposin-negative cells,
saposin B was the most efficient in restoring CD1d recog
99 To gain insight into
saposin B's physiological functions, a specific deficien
100 lex formation between glycosphingolipids and
saposin B, a separate activator protein with broad speci
101 Similar to
saposin B, NPC2 dimers were able to load isoglobotrihexo
102 ort (5 ns) molecular dynamics simulations of
saposin B, starting from both the AB and CD conformation
103 The optimal pH for
saposin B-mediated lipid binding to CD1d, pH 6, is highe
104 Three of these
saposins (
B, C, and D) share common structural features
105 d by creating mice with selective absence of
saposin C (C-/-) using a knock-in point mutation (cystei
106 Saposin C (Sap C) is a small glycoprotein required for h
107 The interaction of
Saposin C (Sap C) with negatively charged phospholipids
108 Saposin C (Trp-free) induced additional activity and flu
109 saposin C, and saposin A [Y30A], poorly with
saposin C [A31Y], and not at all with wild-type saposin
110 Saposin C adopts the saposin-fold common to other member
111 CD spectral changes indicated
saposin C and acid beta-glucosidase interaction only in
112 The CD-/- mice with
saposin C and D combined deficiencies were produced by i
113 e curves demonstrated maximal enhancement by
saposin C and prosaptides at low nanomolar concentration
114 etectable in AB-/- mice, whereas prosaposin,
saposin C and saposin D were expressed near wild-type (W
115 of the conserved saposin A Tyr 30 (Y30) into
saposin C at the analogous position 31, a conserved Ala(
116 s the first representation of membrane bound
saposin C at the atomic level.
117 induces essential conformational changes for
saposin C binding and further enhancement of acid beta-g
118 Saposin C binds to membranes to activate lipid degradati
119 phospholipids or, particularly, phospholipid/
saposin C complexes by intrinsic fluorescence spectral s
120 ibodies directed against the NH2-terminus of
saposin C cross-reacted well with reduced and alkylated
121 The few patients with
saposin C deficiency develop a Gaucher disease-like cent
122 n in LacCer degradation by saposin B for the
saposin C deficiency.
123 t the in vivo effects of saposin C on GCase,
saposin C deficient mice (C-/-) were backcrossed to poin
124 the membrane-binding behavior of a mutant of
saposin C designed to decrease the negative charge of th
125 lized to a 12-amino acid sequence within the
saposin C domain and has been used to derive biologicall
126 ing the neurotrophic sequence located in the
saposin C domain.
127 Deficits in
saposin C enhancement of k(cat) were present in variant
128 In contrast,
saposin C facilitates CD1 lipid loading in a different w
129 hway, acid beta-glucosidase (GCase) requires
saposin C for optimal in vitro and in vivo hydrolysis of
130 These results support the view that
saposin C has multiple roles in glycosphingolipid (GSL)
131 In addition, the deficiency of
saposin C in CD-/- mice resulted in cellular decreases o
132 st, the previously reported NMR structure of
saposin C in the absence of SDS is compact and contains
133 The structure of
saposin C in the presence of SDS is very similar to a mo
134 the three-dimensional solution structure of
saposin C in the presence of the detergent sodium dodecy
135 Conformational changes of
saposin C induced by phosphatidylserine interaction sugg
136 Since
saposin C is a lysosomal protein and pH gradients occur
137 Saposin C is a lysosomal protein needed for optimal GCas
138 Saposin C is a lysosomal, membrane-binding protein that
139 Saposin C is an essential co-factor for the hydrolysis o
140 These data indicate that
saposin C is required for GCase resistance to proteolyti
141 The absence of
saposin C led to moderate increases in GC and lactosylce
142 negatively charged electrostatic surface of
saposin C needs to be partially neutralized to trigger m
143 To test the in vivo effects of
saposin C on GCase, saposin C deficient mice (C-/-) were
144 re present at near wild-type levels, but the
saposin C protein was absent.
145 Across species, this
saposin C region has a high degree of identity and simil
146 udies show that the neuritogenic activity of
saposin C requires specific placement of amino acids, an
147 Loading
saposin C to human PS-/- fibroblasts resulted in an enha
148 We find that the binding of
saposin C to phospholipid vesicles is a pH-controlled re
149 proper orientation of the middle segment of
saposin C to the outside of the membrane surface is crit
150 nesis localized the activation properties of
saposin C to the region spanning residues 47-62.
151 of neurotrophic and activation properties of
saposin C to two different faces of the molecule and sug
152 se neurotrophic and activation properties of
saposin C was elucidated using recombinant or chemically
153 Of the four mature saposins, only
saposin C was found to increase sulfatide concentrations
154 The in vivo effects of
saposin C were examined by creating mice with selective
155 To get insights into
saposin C's function, we have determined its three-dimen
156 the lysosome could be switched on and off by
saposin C's reversible binding to membranes.
157 f the pure enzyme requires phospholipids and
saposin C, an 80 aa activator protein.
158 These results indicate a new property for
saposin C, an anti-proteolytic protective function towar
159 ed and alkylated saposins C and A, wild-type
saposin C, and saposin A [Y30A], poorly with saposin C [
160 A, the corresponding neuritogenic region of
saposin C, and the analogous region of saposin A showed
161 ies to the carboxyl- and NH2-terminal 50% of
saposin C, respectively.
162 logous region of saposin A showed that more "
saposin C-like" molecules had neuritogenic properties.
163 ed only from the lack of GCase activation by
saposin C.
164 is localized to amino acid residues 22-31 of
saposin C.
165 neurite outgrowth in vitro via sequences in
saposin C.
166 resented at acidic pH and in the presence of
saposin C.
167 Wild-type and mutant
saposins C and A from human and mouse were expressed in
168 CD spectra of wild-type and mutant
saposins C and A, the corresponding neuritogenic region
169 ross-reacted well with reduced and alkylated
saposins C and A, wild-type saposin C, and saposin A [Y3
170 paired prosaposin secretion, deficiencies of
saposins C and D and decreases in saposins A and B.
171 r T (iNKT) cells, it remains unclear whether
saposins can facilitate loading of endogenous iNKT cell
172 saposin B as a unreactive backbone, chimeric
saposins containing various length segments of saposin B
173 using recombinant or chemically synthesized
saposin Cs from various regions of the molecule.
174 he complement of disulfide bonds in selected
saposin Cs.
175 Saposin D loading had no effect.
176 B-/- mice, whereas prosaposin, saposin C and
saposin D were expressed near wild-type (WT) levels.
177 In both humans and mice, prosaposin/
saposin deficiencies lead to severe neurological deficit
178 A mouse model of total
saposin deficiency closely mimics the human disease.
179 Saposins,
derived from a common precursor, prosaposin, a
180 embrane interactions and orientations of the
saposins determine the proximity of their activation and
181 Both contain a signal sequence followed by a
saposin domain and a GDSL-lipase domain.
182 In vitro,
saposins extracted monomeric lipids from membranes and f
183 Saposins facilitate this process, but the mechanisms use
184 transfer proteins, such as molecules of the
saposin family, facilitate extraction of lipids from bio
185 mprised of four alpha-helices that adopt the
saposin fold, characteristic of a protein family that bi
186 Saposin C adopts the
saposin-
fold common to other members of the family.
187 elical bundle of granulysin resembles other "
saposin folds" (such as NK-lysin).
188 ic reticulum is complementary to that of the
saposins in endosomes in vivo.
189 plore the in vivo functional interactions of
saposins in GSL metabolism and lysosomal storage disease
190 eate the tissue differential interactions of
saposins in GSL metabolism.
191 osaposin deletion mutants lacking individual
saposins in prosaposin-negative, CD1d-positive cells.
192 In addition, it is unclear whether
saposins,
in addition to loading, also promote dissociat
193 ion of cellular assays and demonstrated that
saposins influence CD1d-restricted presentation to human
194 To determine the
saposins involved in promoting lipid binding to CD1d, we
195 ighlight critical but different roles of the
saposin-
like and cytokine-like domains, including the th
196 cysteine mutations in the amino part of the
saposin-
like domain and in the base of the index finger
197 peptide SP-B(N), derived from the N-terminal
saposin-
like domain of the surfactant protein (SP)-B pro
198 The conserved regions include a
saposin-
like domain, proline-rich domain, and a putative
199 ly related, suggesting that all saposins and
saposin-
like domains share a common topology.
200 SP-B is a member of the
saposin-
like family of proteins, several of which have a
201 nment of deduced J3-crystallin indicates two
saposin-
like motifs arranged in tandem, each containing
202 xpression of Canopy2 (Cnpy2)/MIR-interacting
Saposin-
like protein (Msap) that is known to interact wi
203 t protein B (SP-B) proprotein contains three
saposin-
like protein (SAPLIP) domains: a SAPLIP domain c
204 ilarity to the homologous regions of related
saposin-
like proteins and the importance of the distribu
205 intramolecular disulfide bonds shared by all
saposin-
like proteins.
206 omain with NK-lysin indicates that these two
saposin-
like structures are closely related, suggesting
207 ading lipid antigens without forming soluble
saposin-
lipid antigen complexes.
208 Here we present a
saposin-
lipoprotein nanoparticle system, Salipro, which
209 We suggest that
saposins mobilize monomeric lipids from lysosomal membra
210 Exon 3 encodes a circularly permutated
saposin motif, called a swaposin, found in plant asparti
211 bumins, nonspecific lipid transfer proteins,
saposins,
nematode polyprotein allergens/antigens).
212 Of the four mature
saposins,
only saposin C was found to increase sulfatide
213 ivery of prosaposin (PSAP), the precursor of
saposin peptides that are essential for lysosomal glycos
214 st a crystallin role for the multifunctional
saposin protein family in the jellyfish lens.
215 We found that saposin B forms soluble
saposin protein-lipid complexes detected by native gel e
216 ironment that is stabilized by a scaffold of
saposin proteins.
217 No individual
saposin proved to be absolutely essential, but the absen
218 The deficiency of prosaposin/
saposins (
PS-/-) in humans and mice leads to a decrease
219 he lipid antigen loading machinery genes pro-
saposin (
Psap), Niemann Pick type C2 (Npc2), alpha-galac
220 Importantly, we determined that similar to
saposins,
recombinant NPC2 was able to unload lipids fro
221 s and indicates that the putative primordial
saposin/
swaposin J3-crystallin reflects both the chapero
222 , in tandem, four glycoprotein activators or
saposins,
termed A, B, C, and D, that are essential for
223 espite high sequence homology among the four
saposins,
they have different specificities for lipid su
224 for understanding the contributions of this
saposin to GSL metabolism and homeostasis.
225 tuned over a wide pH range by adjusting the
saposin-
to-lipid stoichiometry, enabling maintenance of
226 These findings reveal how
saposins use different strategies to facilitate transfer
227 When recombinant exogenous
saposins were added to the prosaposin-negative cells, sa
228 We hypothesized that lysosomal
saposins,
which are cofactors required for sphingolipid
229 cystophora), shows similarity to vertebrate
saposins,
which are multifunctional proteins that bridge